The present invention generally relates to wafer alignment for wafer bonding in 3-dimensional (3D) integration processes, and more particularly, to wafer-to-wafer alignment using light emitting diode (LED) and light sensing diode (LSD) devices.
Wafer bonding is a technology used in microelectronics fabrication, in which a first semiconductor wafer having first chip structures may be aligned with second chip structures on a surface of a second semiconductor wafer for fabricating an electronic circuit. The contact may be arranged in such a way that signals may be transported from at least one first chip structure on the first semiconductor wafer to at least one second chip structure on the second semiconductor wafer and vice versa. This arrangement is often referred to as a 3D wafer alignment.
Typically, wafer-to-wafer alignment for wafer bonding may be accomplished through complicated alignment techniques that rely on geometric transpositions of passive structures that represent geometric coordinates on one wafer such that a minimization of an alignment error may be accommodated through external measurement analysis and feedback instrumentation. Such instrumentation relies on optical measurement and detection sensors that predominantly operate in the infrared (IR) or near IR range of the electromagnetic spectrum.
Multiple sources of error may be inherent in this range of the electromagnetic spectrum, such as: refraction of image signal due to possible non-optical linearity of the substrate, opacity of substrate due to metal masking layers, intrinsic error in accuracy due to IR wavelength, etc. As semiconductor technology continues the trend of miniaturization, high-precision wafer-to-wafer alignment becomes increasingly important for 3D integration processes.